宽带、大动态范围RoF系统非线性抑制机理

Radio-over-fiber (RoF) technology is a promising candidate in future access network due to its advantages of large bandwidth, high mobility, and low propagation loss. At present, the nonlinear distortion of the RoF system has become one of the bottleneck of the transmission capacity improvement. When broadband or multiband radio frequency signals are transmitted, the second order distortion and third order intermodulation distortion become the main factors to be considered in the RoF link. However, in the study of high order QAM modulation in RoF links, it has not yet been able to propose a theoretical scheme to completely suppress the above mentioned factors. Therefore, in this project, the large signal analysis model is adopted which consider many nonlinear factors of RoF system with wide-band and large dynamic range. Next, we explore the joint optimization method to suppress the third order intermodulation distortion in the optical domain and to suppress the second order distortion in the digital domain by utilizing the merits of linearization technologies in optical and digital domain, respectively. Through the three stages of theoretical analysis, software simulation and experimental demonstration, we expect to establish a mathematical model which can completely suppress the second order distortion and third order intermodulation distortion, and present a high linearization RoF link implementation scheme. Fillnally, a new broadband RoF access system was built which can further improving the communication capacity and spectrum utilization efficiency.

光纤承载射频（RoF）通信具有大带宽、高移动性和低传输损耗等特点，成为未来接入网极具前景的解决方案之一。目前，RoF系统的非线性失真成为了传输容量提升的瓶颈之一，尤其在宽带或多波段射频信号发射时，二阶非线性失真和三阶交调失真已成为了RoF链路必须要考虑的因素。鉴于在高阶QAM调制RoF链路的研究中，还没有从理论上提出能够完全抑制二阶、三阶失真的一体化方案。因此，本项目拟采用大信号分析模型，将宽带、大动态范围RoF系统的诸多非线性因素合理引入到理论研究中，结合光域线性化方法与数字信号线性化方法的优势，探索在光域抑制三阶交调失真、在数字域抑制二阶非线性失真的联合优化方法。通过理论分析、软件仿真、实验验证三阶段研究，建立起能够完全抑制二阶、三阶非线性失真的数学模型，提出高线性化RoF链路实现方案，构建基于光与无线融合的新型宽带RoF接入系统，进一步提升系统通信容量和频谱利用效率。

光纤承载射频（RoF）通信融合了光纤通信容量大和移动通信可随机接入的优点，具有传输速率高、可利用频带宽、保密性强等优点，有望为下一代无线通信网络提供Tbps数量级的移动数据传输。由于RoF系统的非线性失真成为了传输容量提升的瓶颈之一，本项目在“光域线性化”和“数字信号线性化”两个方面开展了研究工作，分别将宽带、大动态范围RoF系统的诸多非线性因素引入到理论研究中，结合这两个方面的技术结合优势，通过理论分析与建模、仿真与测试、原理性实验验证等三阶段研究，阐明了RoF链路系统中的非线性抑制机理，建立起了大动态范围内抑制非线性失真的数学模型，提出了高线性化RoF链路实现方案，构建了基于光无线融合的新型宽带RoF验证系统。取得的重要结果如下：（1）光域线性化方面。围绕抑制RoF系统链路中的二阶和三阶非线性失真问题，提升系统的无杂散动态范围（SFDR），提出了三种高线性化方案，实现了二阶谐波失真和三阶交调失真的有效抑制，将系统的SFDR提升到127dB以上；（2）数字域线性化方面。围绕传输链路中的非平坦频率响应、多径效应，光纤传输的线性和非线性损伤等问题，提出了偏振复用单边带QAM信号产生方案，实现了毫米波信号在传输过程中对光纤色散不敏感，从而有效克服了信号的走离效应等问题；（3）光域线性化与数字线性化结合方面。针对信号调制速率受到电放大器性能以及数模转换器（DAC）带宽的限制，提出了两种光子矢量信号产生方案，第一种是无需DAC装置的概率整形光16QAM信号产生方案，第二种是基于开关键控调制的光载矢量毫米波正交相移键控信号产生方案。这两种方案具有无需预编码技术和数模转换器的特点，从而降低了信号处理复杂度和系统成本。本项目研究成果丰富和完善了RoF系统方案，进一步提升了系统的传输容量和频谱利用效率。